Most conventional magnetic recording mediums are produced using a binder of a thermoplastic resin such as vinyl chloride acetate resin, vinyl chloride/vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, and acrylonitrile butadiene resin, which are used either alone or in combination. However, one defect of such mediums is that the magnetic layer is unsatisfactorily wear-resistant and tends to foul the tape transport path.
Methods are known that use a thermosetting resin such as melamine resin or urea resin or blend the thermoplastic resins described above with a binder that forms crosslinkages by chemical reaction, such as an isocyanate compound or an epoxy compound. However, such crosslinkable binders have two important disadvantages: (1) the resin solution having magnetic particles dispersed therein does not have long keeping quality (i.e., has a short pot life) and the resulting magnetic coating composition, and hence the magnetic tape, tends not to have consistent physical properties; and (2) after drying the applied magnetic coating composition, it must be heated for curing, and this results in prolonged processing time.
To overcome these disadvantages, Japanese Pat. No. 12423/72 and Japanese patent application (OPI) Nos. 13639/72, 15104/72 and 77433/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") purpose methods for producing a magnetic recording medium which use a binder of an acrylate ester oligomer and monomer and cure the dried magnetic coating composition by irradiation with electron beams. However, such methods are not capable of producing a magnetic recording medium having good electrical characteristics and mechanical properties.
There has been an increasing demand for providing magnetic recording media with better electrical characteristics by using a magnetic coating composition comprising a good dispersion of ferromagnetic particles. A poor dispersion of ferromagnetic particles can cause low output or noise. The conventional method of curing the magnetic coating composition by electron beams is not satisfactory since if a high concentration of magnetic particles are contained therein to achieve higher-density recording, the resulting magnetic coating composition has a short pot life and cannot provide a magnetic tape having electrical characteristics that withstand practical use. On the other hand, a thin base is required for achieving extended recording, and to meet this requirement, the mechanial properties of the magnetic coating composition must be improved.
Furthermore, with the use of multi-functional video cassette recorders, there has been a demand for video tape that withstands service under hostile conditions, but it has not yet been possible to prepare a magnetic recording medium having sufficiently satisfactory mechanical properties.